Method of manufacturing wire



I H J- dntteo states 3,262,293 Patented July 26, 1966 3,262,293 METHOD OF MANUFACTURING WIRE Martin B. Maclnnis, Towanda, Pa., assignor to Sylvania Electric Products Inc., a corporation of Delaware No Drawing. Filed May 25, 1964, Ser. No. 370,108

4 Claims. (Cl. 72-42) This invention relates to a method of producing wire. More particularly, it relates to an improvement in the process of drawing wire through one or more dies to mechanically work it to a desired final diameter.

In the procedures heretofore generally employed in wire drawing it has been the practice to subject the wire to several treatments or process steps prior to pulling it through each die. Referring, for example, to the production of tungsten wire, in the first of these steps, the wire is rapidly heated to a temperature sufiiciently high to develop a layer of tungsten oxide on the surface of the wire. Typically, tungsten wire is passed through a gas liame which is sufiiciently intense to heat the wire almost instantly to temperatures of the order of 800 to 1000 C. At these temperatures an oxide coating is formed on the surface of the wire, the purpose of the coating being to afford a surface to which a die lubricant, applied in the subsequent step, will adhere.

After the oxide layer is established on the wire, the die lubricant is applied. Generally, the lubricant is in the form of an aqueous suspension or emulsion containing colloidal graphite, and the application is accomplished by passing the wire through a bath of the lubricant composition. In addition to reducing the wear on the die, the graphite which adheres to the wire forms a protective coating for protection of the wire from further oxidation when it is heated to the temperature required for reduction in diameter in the next die in the series. During this second heating operation the graphite coating is baked on the surface so that it will adhere sufficiently to afford the necessary lubricating action as the wire moves through the die.

The method of drawing wire as described above has been open to a number of objections which stem primarily from the necessity for heating the wire to produce the oxide coating. There is a tendency for the oxide coating to be non-uniform which, in turn, causes a non-uniform coating of the subsequently applied lubricant. As ultimate results, substantial die wear is experienced, and the wire may exhibit non-uniform diameter and physical properties. Furthermore, the additional heating step causes loss of valuable material. Part of this loss is attributable to the excessive oxidation found to be necessary to insure at least a minimum continuous oxide coating. Additional loss of material results from volatilization of the ingredients of the wire or oxides of the ingredients at the oxidation temperature.

It is, therefore, an object of this invention to provide an improved method for drawing wire which affords wire of increased uniformity of dimensions and physical characteristics.

It is a further object .of the invention to provide a iethod of drawing wire which permits elimination of the high temperature oxidation of the wire preliminary to application of a lubricant coating.

A still further object of the invention is to provide a method of drawing wire which involves substantially less die wear than has been experienced in wire drawing methods heretofore employed.

The foregoing objects are accomplished in accordance with the method of the present invention by oxidizing the wire surface by means of an aqueous solution of an oxidizing agent in lieu of the heating ope-ration heretofore employed. The solution may be applied to the surface of the wire in various manners. However, it is preferred to pass the wire through a bath of the solution. Although various water-soluble oxidizing agents known to those skilled in the art may be employed, it is essential that the oxidizing agent selected for use with any particular metal wire be such that the oxide formed on the wire is substantially insoluble in the solution of the oxidizing agent. Potassium permanganate, for example, has been found particularly useful as an oxidizing agent in the application of the present process to tungsten wire.

As can readily be appreciated the thickness of the oxide layer may be readily controlled by varying the length and rate of passage of the wire through the oxidizing solution and the concentration of the oxidizing agent in the solution. Furthermore, an uninterrupted oxide coating is obtainable even though only a thin layer of the oxide is applied. Since the wire is not subjected to any thermal extremes until after the lubricant is applied in the subsequent operation, there is a minimum of tendency for the oxide to flake off, exposing bare metal to which the lubricant will not adhere.

After the wire passes from the bath of the oxidizing solution, it may be passed directly to a station at which the lubricant is applied. Typically, the lubricant is colloidal graphite in an aqueous medium. Alternatively, in the interest of minimizing contamination of the lubricant bath and the lubricant coating on the wire, the wire may be passed through a spray or bath of water to remove the by-products of the oxidation of the wire prior to application of the layer of lubricant material.

After the wire has received a coating of lubricant it passes continuously through a heating zone and is heated to whatever elevated temperature is required for work ing during passage through the reducing die. As indicated above, in connection with the description of the wire drawing processes heretofore employed, no appreciable oxidation of the wire occurs during this heating op e-ration since the surface of the wire is protected by,the lubricant layer.

As an illustration of the method of the invention, tungsten wire of 1.565 mils diameter was reduced to wire of 1.420 mils diameter in the manner described below.

Tungsten wire of 1.565 mils diameter was continuously drawn from a supply spool and was passed through a bath containing an aqueous potassium permanganate solution of approximately 0.1 Normal concentration. The wire was drawn through the bath at a rate of about feet per minute and about 24 inches of the path of movement of the wire was below the surface of the bath, so'

that each increment of the wire was exposed to the oxidizing potassium permanganate solution for a period of about 1.5 seconds. As a result of the reaction of the potassium permanganate solution 'on the metal of the wire surface, a thin but continuous coating of tungsten oxide was observable on the surface of the wire leaving the bath.

The wire was next passed through a bath of an aqueous emulsion containing colloidal graphite. This particular lubricant material is generally available on the market under the trade name Aquadag. Examinaton of the wire leaving the lubricant bath indicated that the surface was uniformly wet by a continuous film of the lubricant.

The coated wire next was passed through a gas flame and was rapidly heated to a temperature of about 800 C. as measured by an optical pyrometer. At this temperature, the graphite coating was rapidly dried and baked on the wire surface to produce an adherent graphite film, and the wire was immediately drawn through a reducing die designed to work the diameter of the wire down to the desired dimension of 1.42 mils. Examination of the resulting Wire showed it to be of uniform cross-section O and free of flattened sections heretofore frequently characteristic of wire drawn by processes in which the oxide coating used as a base for the layer of lubricant was applied by heating the wire to an elevated temperature in air.

What is claimed is:

1. The method of mechanically working metal wire to a desired diameter which comprises the steps of contacting the wire with an aqueous oxidizing solution capable of oxidizing the metal of the wire to a metal oxide insoluble in the solution, thereby forming on the wire an adherent layer of the metal oxide; applying a coating of a die lubricant over the oxide layer on the wire; heating the wire to working temperature; and thereafter drawing the wire through a reducing die.

2. The method of mechanically working metal wire to a desired diameter which comprises the step of passing the wire through an aqueous oxidizing solution capable of oxidizing the metal of the wire to a metal oxide insoluble in the solution, thereby forming on the wire an adherent layer of the metal oxide; water-rinsing the wire to remove by-products of the oxidation of the metal of the wire by the oxidizing solution; passing the wire through an aqueous suspension of die lubricant; heating the wire to working temperature; and thereafter drawing the wire through a reducing die.

3. The method of mechanically working tungsten wire to a desired diameter which comprises the steps of contacting the wire with an aqueous solution of potassium permanganate to form on the wire an adherent layer of tungsten oxide; applying a coating of graphite over the oxide layer; heating the wire to working temperature; and thereafter drawing the wire through a reducing die.

4. The method of mechanically working tungsten wire to a desired diameter which comprises the steps of passing the wire through an aqueous potassium permanganate solution of 0.1 Normal concentration to form on the wire an adherent layer of tungsten oxide; water-rinsing the wire to remove by-products of the oxidation of the tungsten; passing the wire through an aqueous suspension of graphite to provide a coating of graphite on the layer of tungsten oxide; heating the wire to a temperature of about 300 C.; and thereafter passing the wire through a reducing die.

References Cited by the Examiner UNITED STATES PATENTS 1,022,182 4/1912 Dempster 7242 1,076,590 10/1913 Liebmann 7242 1,253,362 1/1918 Farkas.

2,120,496 6/1938 Hauger 7242 2,369,596 2/1945 Millen 7246 2,709,516 5/1955 Trembicki 205--21.1 3,118,330 1/1964 Geipel 7246 CHARLES W. LANHAM, Primary Examiner.

H. D. HOINKES, Examiner. 

4. THE METHOD OF MECHANICALLY WORKING TUNGSTEN WIRE TO A DESIRED DIAMETER WHICH COMPRISES THE STEPS OF PASSING THE WIRE THROUGH AN AQUEOUS POTASSIUM PERMANGANATE SOLUTION OF 0.1 NORMAL CONCENTRATION TO FORM ON THE WIRE AN ADHERENT LAYER OF TUNGSTEN OXIDE; WATER-RINSING THE WIRE TO REMOVE BY-PRODUCTS OF THE OXIDATION OF THE TUNGSTEN; PASSING THE WIRE THROUGH AN AQUEOUS SUSPENSION OF GRAPHITE TO PROVIDE A COATING OF GRAPHITE ON THE LAYER OF TUNGSTEN OXIDE; HEATING THE WIRE TO A TEMPERATURE OF ABOUT 800* C.; AND THEREAFTER PASSING THE WIRE THROUGH A REDUCING DIE. 